1. Field
The present inventions relate generally to systems and methods for reducing acid and metal emissions from combustion systems and, more particularly, to boosted no-lance injection systems and methods to reduce acid and metal emissions.
2. Related Art
Combustion systems having boilers are known in the art and can include, for example, pulverized coal plants, circulated fluidized beds, gas-fired systems, oil-fired systems, waste incinerators, direct-fired process heaters, kilns, tangentially-fired boilers, etc. Common elements of various combustion systems typically include a combustion chamber and a burner for igniting fuel located in the combustion chamber. Fuel (e.g. coal or biomass) is fed into the combustion chamber, where it is rapidly ignited and stabilized on burners. Any of a number of undesirable components included in the fuel, e.g. acid components or metal components, may enter the environment via flue gas exiting the stack and may cause any number of undesirable consequences. Examples of undesirable acid components in the flue gas include sulfur dioxide (SO2), sulfur trioxide (SO3), sulfuric acid (H2SO4), hydrogen chloride (HCl), hydrogen bromide (HBr), hydrogen fluoride (HF), chlorine (Cl2) and bromine (Br2). Examples of undesirable metal components in the flue gas include antimony (Sb), arsenic (As), beryllium (Be), cadmium (Cd), chromium (Cr), cobalt (Co), lead (Pb), manganese (Mn), mercury (Hg), nickel (Ni), and selenium (Se). The current state-of-art of dispersing or mixing solid sorbents into a flue gas for capture of acid gas and metal pollutants uses a plurality of injection lances.
FIG. 1 illustrates one example of a combustion system referred to generally as system 2, using a traditional technique to reduce the emission of an acid component. In this example, the traditional technique is based on the use of several lances 4 extending deep into the ductwork 6 (enlarged for viewing) of system 2. Lances 4 are used to inject dry sorbent into flue gas traveling through ductwork 6, and can achieve some success at reducing undesirable components in the flue gas. Applicants, however, are generally dissatisfied with existing lance systems.
Applicants believe that lance systems can suffer from any number of problems, which Applicants would like to improve. For example, lance systems may warp over time because of heat exposure, thereby promoting clogging, adversely affecting sorbent dispersion, increased maintenance costs and prohibiting removal of the lance for maintenance without a unit outage. Further, lance systems may overheat the sorbent, thereby clogging the lance or reducing sorbent utilization. In addition, lance systems may fail to properly distribute sorbent for desired efficacy.
When a greater percentage of capture pollutants is desired, additional lances are often added in attempt to distribute the sorbent across the cross-section of the flue gas duct. Applicants believe this strategy creates additional problems. For example, as the number of injection lances increase, evenly distributing the sorbent to multiple injection lances becomes mechanically complex. The sorbent is transported to the vicinity of the flue gas duct by a limited number of air streams, for example one or two air streams. In order to provide multiple injection lances, a single transport air stream must be evenly divided into multiple streams. Such division suffers from an inability to divide the sorbent stream evenly, and the number of division points increases the likelihood of plugging with the solid sorbent downstream of the division points. Also, as the number of injection lances increases, the total amount of transport air used increases in proportion to the number of lances because a certain minimum velocity of air must be maintained within each lance to minimize likelihood of plugging with the solid sorbent, for example, a minimum of 15 m/s. This increased air flow load requires that the transport pipe, air blowers and associated blower air conditioning equipment size must be increased.
Further, lance systems may result in undesirable flue gas pressure drops because of the depth of penetration of the lances and numbers of the lances.
In-duct mixing devices, such as baffle plates, can also be used in conjunction with lance injection systems to increase mixing of sorbent and flue gas. However, Applicants believe that the application of in-duct mixing devices requires extended and unnecessary shutdown of the combustion unit for installation. Moreover, Applicants believe that in-duct devices cause a significant and unnecessary gas pressure loss, which permanently increase operating cost. Further, in-duct devices can also accumulate sorbent deposits or solids from the combustion system, thereby leading to shutdown of the combustion system for cleaning of the in-duct device.
These problems, Applicants believe, result in excessive or unnecessary maintenance, operational costs and offline requirements. Further, these problems may result in non-compliance with emissions regulations, and further increase costs and reduce power output.
Additionally, as illustrated in FIG. 1, for lances to perform effectively for a desired duration, lances are almost always need to be placed in a vertical orientation to reduce additional warping caused by gravity. Applicants are generally dissatisfied with the vertical orientation of lance systems, because Applicants believe the vertical orientation of lance systems place unnecessary constraints on system design, access, maintenance, and efficacy.
Accordingly, the present inventions are directed to at least one of these, or additional problems.